1. Field of the Invention
The present invention relates generally to apparatus for protecting a sensor or manometer, and, more particularly, to an apparatus for protecting a pressure differential sensor from exceeding a maximum allowable pressure differential.
2. Description of the Prior Art
The prior art discloses a system in which a flap valve is maintained open by a back pressure which is selected such that the flap valve can close the upstream circuit when the pressure in the circuit becomes greater than the back pressure, thus assuring protection of an absolute pressure sensor positioned downstream.
Unlike absolute pressure sensors, differential pressure sensors or differential manometers are adapted to measure a difference in pressure between two fluids. It is possible to protect the high-pressure circuit against overloads, by a system of the type described above. It is not possible, however, with this type of protection system, to safeguard the sensor against a differential pressure which is so great that it would present the risk of damaging the sensor.
Differential sensors are generally made of very costly materials. Protecting them is particularly delicate, because it is necessary to take into account not a pressure, but the difference between two pressures.